This invention relates to a temperature controller for automobile air conditioner, and particularly to a temperature controller for automobile air conditioner suitable for automatically controlling the temperature of air delivered from the air conditioner.
Automobile air conditioners which have been provided separately as a cooler unit and a heater unit tend recently to integrate these units, establishing a reheat-air mix system which is superior in the continuous temperature control property and also provides an extra dehumidification function. An automobile air conditioner of the reheat-air mix type operates in such manner that target opening am of an air mix door is determined from the difference between the target delivered air temperature Tdo and the actual delivered air temperature Td, and the opening of the air mix door is controlled so that the voltage produced by a potentiometer which responds to the movement of the air mix door is consistent with the target value .theta..sub.am, thereby attaining the target temperature .theta..sub.am, as disclosed in Japanese Patent Unexamined publication No. 58-136509 for example.
The same applicant as of the present invention proposed, in U.S. patent application Ser. No. 093,228 on Sept. 4, 1987, a temperature controller for automobile air conditioner, which does not use a feedback potentiometer for detecting the opening of the air mix door, but operates to vary the opening of the air mix door in response to the target delivered air temperature Tdo and actual delivered air temperature Td so that the delivered air temperature Td is brought close to the target temperature Tdo.
Among the above-mentioned conventional temperature controllers for automobile air conditioner, the one using a feedback potentiometer for implementing control, which is based on the information on the opening of the air mix door, achieves a stable control even in the presence of nonlinear sections in the characteristics of the heat exchanger. On the other hand, however, this system necessitates a link mechanism between the feedback potentiometer and air mix door and its adjustment at assembly, and further necessitates the calculation of the target opening .theta..sub.am, the analysis of the voltage signal from the potentiometer, and the process for compensating the variability of characteristics between the opening of air mix door and the rotational angle of potentiometer, resulting in an increased complexity of control specifications. In consequence, when microcomputer-based control is intended, it needs an increased program loading area, which raises the manufacturing cost along with the above-mentioned intricacy of adjustment work and also deteriorates the reliability and durability of the controller due to an increased number of component parts.
Whereas, the above-mentioned system, which was proposed by the applicant of the present invention with the intention of controlling the delivered air temperature Td more directly without using a potentiometer for detecting the opening of air mix door, is simpler in structure and lower in manufacturing cost. However, it leaves a problem in that accurate control and thus stable control is not achieved if a unit variation in the heat exchange output for producing a unit variation in the delivered air temperature Td is not unique due to the nonlinearity of characteristics of the heat exchanger.